Dental Caries Demineralization of the tooth surface caused by bacteria Chemicoparasitic theory (1890) ● Proposed in 1890 by W. D. Miller in his book "The microorganisms of the human mouth" based upon the work done in Robert Koch’s laboratory in Berlin ● Acid and parasite ● Showed that the degradation of carbohydrate-containing foods resulted in acid formation and was able to demonstrate this process in vitro with isolated oral bacteria and extracted teeth. ● Concluded that dental caries was caused by multiple species of oral bacteria ● No specific bacteria was implicated – “non-specific” Miller’s Conclusion ● Dental caries was caused by multiple or all species of oral bacteria “Non-specific plaque hypothesis„ ● Proper prevention is therefore is to remove or minimize multiple bacterial species. Practice of tooth brushing, flossing and professional tooth cleaning. The specific plaque hypothesis and dental caries ● In 1924, Clark isolated streptococci from human carious lesions, and named Streptococcus mutans ● In 1960, Keyes showed that ‘caries-free’ hamsters develop dental caries only when caged together with ‘caries-active’ hamsters - Infectious and transmissible ● The bacteria previously referred to as S. mutans are actually seven distinct species now called mutans streptococci (MS) ● MS are the principal etiological agents of dental caries Microbial etiology of dental caries Mutans Streptococci (MS) Requires a relatively high proportion (2-10%) of mutans streptococci within dental plaque. Possess adherence activity (to tooth surface) Produce higher amounts of acid from sugars than other bacterial types, and possess acid tolerance Produce extracellular polysaccharides from sucrose. ● Lactobacilli Dentin, root caries, acidogenic, acid tolerant ● Actinomyces viscosus Acidogenic and acid tolerant Current diagnosis and treatment ● Future diagnostics using microbiology Detection and monitoring of cariogenic bacteria others ● Potential preventive measures based on microbiological principle Preventing bacteria from colonizing tooth surface Local and topical antimicrobial agents Replacement therapy Mutans Streptococci Early acquisition and transmission ● Mutans streptococci appear in the mouth after teeth have erupted as they need solid surfaces to colonize. ● The establishment of the bacteria seems rather slow the first two years, and one talks about a "window of infectivity" which would open after about two years. ● There seems to be a family pattern as similar types of bacteria have been found in the mouth of child and parents, in particular mothers. Mutans Streptococci - prevalence ● Global distribution – found in all populations ● High counts - 106/ml saliva ● Usually, serotype c (Streptococcus mutans) is the dominating serotype. One person can have several serotypes (both Streptococcus mutans and Streptococcus sobrinus). Dental caries in relation to mutans streptococci Lactobacilli ● Gram-positive bacteria which are commonly isolated from the oral cavity. ● Cariogenic, highly acidogenic organisms, however, has low affinity for tooth surfaces. ● Associated more with carious dentine and the advancing front of caries lesions rather than with the initiation of the disease. ● Usually lactobacilli comprise less than 1% of the total cultivable microflora. However, their proportions and prevalence may increase at advanced caries lesions both of the enamel and of the root surface. Sugar metabolism of cariogenic bacteria ● Acid production (lactate) from glucose and fructose ● Formation of extracellular polysaccharides (glucose polymer, fructose polymer) from the energy of the disaccharide bond of sucrose. (glucosyltransferase, fructosyltransferase) - Increase the thickness of plaque substantially - Changing the chemical nature of its extracellular space from liquid to gel. - The gel limits movement of some ions, protects the plaque biofilm from salivary buffering. Plaque which has not had contact with sucrose is both thinner and better buffered. The metabolism of S. mutans ● Key to the pathogenesis of dental caries - The fermentation of these carbohydrates is the principal source of energy for S. mutans Genome sequence shows that S. mutans can metabolize a wider variety of carbohydrates than any other G(+) microorganism - The glycolytic pathway leads to the production of pyruvate, to lactic acid (by LDH activity), formate, ethanol and acetate - The acidic environments are responsible for the damage of tooth structure - Acid tolerant – based on a membrane-bound, acid stable, proton-translocating ATPase Virulence factors of S. mutans ● Production of acid ●Adhesins Wall-associated protein A (WapA) S. mutans LraI operon (SloC) Glucan-binding proteins A and C ●Adherence mechanism Two methods of attachment ● Sucrose independent –using ionic and lectin like interaction - Adhere to salivary agglutinin glycoprotein (SpaP: Streptococcal protein antigen P, aka antigen I/II) - Isogenic mutants of SpaP - Passive immunization study - Adhere to other bacteria, the extracellular matrix and epithelial cell-surface receptors Two methods of attachment ● Sucrose dependent - Adhere to tooth surface by synthesizing glucans by glucosyltransferases - Glucan promotes cell-cell aggregation by interacting with surface-associated glucan binding protein Virulence factors of S. mutans Ecological basis of dental caries ● Environmental changes A variety of environmental signals in complex communities ● Ecological shift The signal triggers adaptation to acid environment ● Biofilm characteristics Virulence properties of S. mutans ● Adhesion, acidogenicity, and acid tolerance ● Each of these properties works coordinately to alter dental plaque ecology. ● The ecological changes are characterized by increased proportions of S. mutans and other species that are similar lacidogenic and aciduric. ● The selection for a cariogenic flora increases the magnitude of the drop in pH following the fermentation of available carbohydrate and increases the probability of enamel demineralization. Novel approach to dental caries Replacement therapy ● Replacing a specific bacterial pathogen with a non- pathogenic strain, an effector strain - should not cause disease itself or disrupt the ecosystem to other disease state - must persistently colonize the host tissue at risk and thereby prevent colonization or outgrowth of the pathogen - should possess a high degree of genetic stability ● Possible life-long cavity protection ● Little or no risk of side effects ● Minimal patient education and compliance Replacement therapy for the prevention of dental caries ● Lactate dehydrogenase (LDH)-deficient mutants Streptococcus rattus LDH mutants were shown to have little or no cariogenic potential in vitro and in various rodent models. ● Lantibiotic production S. mutans strain (JH1000) produces a lantibiotic called mutacin 1140 capable of killing virtually all other strains of mutans streptococci against which it was tested.
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